Acquisitions, Dispositions and Other Significant Transactions - HCP Master Lease Transaction and RIDEA Ventures Restructuring (Details) $ in Thousands			1 Months Ended				3 Months Ended		12 Months Ended		15 Months Ended
	Jan. 01, 2018 USD ($) community	Nov. 01, 2017 community joint_venture	Apr. 30, 2018 USD ($) community	Mar. 31, 2018 USD ($)	Jan. 31, 2018 USD ($) community	Dec. 31, 2017 USD ($) joint_venture	Mar. 31, 2019 USD ($) lease community	Mar. 31, 2018 USD ($)	Dec. 31, 2019 community	Dec. 31, 2018 USD ($) community	Mar. 31, 2019 USD ($) lease
Business Acquisition [Line Items]
Number of communities leased | lease							251				251
Gain (loss) on sale of assets, net | $							$ (702)	$ 43,431
Non-cash management contract termination fee | $							$ 353	$ 2,242
Master Lease Transactions
Business Acquisition [Line Items]
Annual rent reduction | $	$ 2,500
Number of communities with rent reduction	2
RIDEA Ventures Restructuring
Business Acquisition [Line Items]
Number of communities management is retained			18
HCP, Inc. | Master Lease Transactions
Business Acquisition [Line Items]
Number of communities acquired										2
Payment to acquire leased assets | $										$ 35,400
Number of communities leased										43
HCP, Inc. | RIDEA Ventures Restructuring
Business Acquisition [Line Items]
Number of communities acquired			3		1
Payments to acquire asset from joint venture | $			$ 207,400		$ 32,100
RIDEA Ventures | RIDEA Ventures Restructuring
Business Acquisition [Line Items]
Percentage ownership				10.00%		10.00%		10.00%
Number of joint ventures | joint_venture		2				1
Proceeds from sale of joint venture interest | $				$ 62,300		$ 32,100
Gain (loss) on sale of assets, net | $				$ 41,700
Number of communities managed		59
33 Communities Disposed Of Through Lease Terminations | HCP, Inc. | Master Lease Transactions
Business Acquisition [Line Items]
Number of communities disposed of										33
37 Communities Disposed Of Through Operations and or Management Termination | RIDEA Ventures Restructuring
Business Acquisition [Line Items]
Number of communities disposed of							37
34 Communities Disposed Of Through Management Termination | RIDEA Ventures Restructuring
Business Acquisition [Line Items]
Number of communities disposed of							34
Non-cash management contract termination fee | $							$ 400	$ 2,200			$ 9,100
3 Communities Disposed Of Through Management Termination | Forecast | RIDEA Ventures Restructuring
Business Acquisition [Line Items]
Number of communities disposed of									3